Shortest Subsequence#11422
You are given a DNA sequence consisting of characters A, C, G and .
Your task is to find the shortest DNA sequence that is not a subsequence of the original sequence.
One line contains a DNA sequence with n~(1 \le n \le 10^6) characters.
Print the shortest DNA sequence that is not a subsequence of the original sequence. If there are several solutions, you may print any of them.
Example 1